Stabilizing arrangements for floating bodies



Feb. 4, 1969 J. BELL 3,

STABILIZING ARRANGEMENTS FOR FLOATING BODIES Filed Sept. 11,. 1967 Sheet1 of 2 Feb. 4, 1969 J. BELL 3,425,384

STABILIZING ARRANGEMENTS FOR FLOATING BODIES Filed Sept. 11, 1967 She et2 of 2 United States Patent 46,950/ 66 US. Cl. 114-125 Int. Cl. B63b43/06 Claims ABSTRACT OF THE DISCLOSURE A floating member in the liquidin a tank moves from side to side of the tank with the ships roll and bydisplacing the liquid in the tank stabilizes the ship. The floatingmember is free to move from side to side and moves in a path ofpronounced curvature.

This invention relates to stabilizing arrangements for bodies floatingin liquids e.g. ships floating in Water, by which the body is stabilizedagainst periodic rolling action.

It is known to do this by incorporating tanks in the body so that liquidflows from one side to the other under the periodic rolling motion ofthe body but out of phase therewith so as to dampen the rolling motion.

Tan-k systems are normally constituted of two tanks approximately thesame size, on either side of the vessel, connected by a channel andpartly filled with liquid so that the stabilizing liquid will flow fromone tank to the other under the influence of the movement of the ship.

Various designs of tanks are known and the shape of the tank may bevaried, as also the connecting channel between; for example, somechannels have restrictive features causing resistance to the flow of theliquid, and others may have valves which control according to a sensingdevice the flow of the liquid. But in all the hitherto known designs theconfiguration of the tank and its connecting channel are fixed, orsemi-permanent; in other words, the size of the tanks and channel doesnot change with the rolling motion of the vessel.

In one aspect the present invention consists in a tank system forstabilizing a floating body against periodic rolling motion, comprisinga tank containing liquid, and a member floating therein and free to moveover a range within the tank to vary the distribution of the liquidalong the tank, i.e. athwartships in the vessel to be stabilized.

For an efficient system of this type the floating member would ideallyhave no mass, but the efliciency of the system is such that a mass of upto say 30% or thereabouts of the equivalent volume of the liquid in thetank can be accepted.

The floating member may be constrained to move in accordance with thedesigned features of the tank or otherwise and in accordance with anydesired law, and the shape of the floating member may be designed eitherfor simplicity or high efiiciency; for example, the simplest form offloating member would be a sphere or cylinder.

Preferably the tank system is contained in a compartment or portion ofthe vessel which is roughly rectangular in shape, although variationsfrom this shape can readily be accommodated without affecting theoperation of the system.

In the event the tank system is a closed one, an air or gas-filled spaceis generally provided above the liquid surface. The air or gas pressuremay be near, or above or below atmospheric pressure.

The level of liquid surface in the tank system may be varied oralternatively the tank system may be completely filled and if desiredmay be arranged to be open, or openable to the liquid surrounding thebody to be stabilized, e.g. the sea.

The variation in level may be used to regulate the oscillation period.

Also, the period and power may be regulated by filling the floatpartially with liquid, e.g. by means of flexible pipes attached thereto.

The invention will be further described with reference to theaccompanying drawings, in which:

FIGURE la is a cross-section of a tank system according to the inventionwhen the floating body containing it is in a neutral position;

FIGURE lb is a similar view with tilted to one side.

FIGURE 2a is a view similar to FIGURE 1a 'with an alternative form offloating or buoyancy member;

FIGURE 2b shows the tank system of FIGURE 2a in the position in whichthe associated floating body is tilted to one side.

FIGURE 3a is a view showing a variation of the tank arrangement ofFIGURE 2a; and

FIGURE 3b shows the same arrangement in the tilted position of thefloating body;

FIGURE 4a is a similar view to FIGURE la showing another form offloating member, and

FIGURE 4b is another view of the same corresponding to the tiltedposition of the associated floating body.

FIGURE 5a shows a variation of the FIGURE 4a system, and

FIGURE 5 b is the same in the tilted position.

FIGURE 6 is a cross-section of a tank stabilizing system according tothe invention;

FIGURE 7 is a similar view of a modified system;

FIGURE 8 is a similar view of an alternative system;

FIGURE 9 is a similar view of a still further system.

Referring to FIGURES la and 1b, a tank 1 of rectangular shapesubstantially full of water having a free surface and containing asphere 2, which is buoyant and presses up against the top of the tankdue to the buoyancy of the liquid, the roof or top 1a of the tank is ofbarrel vault shape. With the vessel in which the tank is mounted on aneven keel the sphere will be in the centre. With a heel or movement ofthe vessel the sphere 2 will move to one side or the other as shown inFIGURE lb, and in doing so will displace the stabilizing liquid in theopposite direction. This movement of the liquid in a known tunedperiodic manner 'will therefore cause a stabilizing moment to be exertedon the vessel.

In the arrangement shown in FIGURES 2a and 2b, the sphere 2 has beenreplaced by a rectangular body 3, supported by a system of wheels orrollers 4 within or attached to the rectangular body, the said wheels orrollers 4 being pressed against the curved roof of the tank.

As shown in FIGURES 3a and 3b, the roof of the tank or part thereof ismade in an alternative form consisting of two cam or curved surfacesagainst which the wheels or rollers 4 bear, the position of therectangular body being controlled by the tilt of the vessel and thecontour of the cam surfaces.

FIGURES 4a and 4b show a similar rectangular member 3 which in this caseis secured to the bottom of tank 1 by two sets of parallel spaced links5.

the floating body As shown in FIGURES a and 5b the links 5 instead ofbeing parallel would be inclined towards each other from top to bottom.

The cross section of the tank system only is shown in the drawings; thelength in the fore and aft direction will depend on the value of thestabilizing moment required in any given application.

This novel tank system has been called a Buoyant Passive Tank because ofthe movable floating or buoyant member.

In common with previously known tanks, the Buoyant Passive Tank istunable and will resonate at a given periodic time depending on a numberof design features. For example, in FIGURES 1a and 1b the tuning willdepend on the density of the fluid, the density of the sphere, thedimensions of the tank and sphere and the radius of curvature of theupper part of the tank. A much wider scope for tuning is thus providedthan in previously known passive tank system.

Referring to FIGURE 6, there is a tank system 1 containing a float 3having wheels 4 and oscillating from side to side on a suitably shapedcam system 6 the height of which may be adjusted from a motor 7operating over gears 8 and threaded members 9 passing through the top ofthe tank 1 to engage the cam system 6.

A stop pin 10 is provided to engage in a recess in the upper surface ofthe float for the purpose of locking the float centrally (or in anyother predetermined position).

In FIGURE 7 there is shown a similar arrangement but with a singlethreaded member control centrally located instead of the two spacedthreaded members of FIGURE 6. Also the cam system 6 is formed of twomembers hinged together, the threaded member 9 operating on the hingepin 6a.

In FIGURE 8 is shown a system similar to that of FIGURES 2a and 2b butin this case with the tank system shown completely filled and providedwith slide doors or valves 11 at the side for passage of liquid fromsurrounding sea.

The floating member may be arranged (although not shown on diagram) tobe held closely to the tank bottom, so that the amount of water notcontributing to stabilization is reduced to a minimum and water flows inand out through the open slide doors 11.

According to the use of various cams or linkages, the floating membermay be moved in any way desired, ie. it can be moved parallel to tankbottom or tilted with respect to it.

The sea openings may be positioned as desired and the openings fittedwith slide doors or valves. The slide doors or valves may be adjustableto regulate the flow of water in any desired manner.

The tank will thus be tunable by adjustment of the controls or cam shapeor by adjustment of the sea opening. A combination of two or more ofthese methods may be used if so desired.

The loss of metacentric height due to the free surface eflect compoundedin this system with the movement of the buoyant member is controlled bythe design of cam as is also the sensitivity of the stabilizer. In thisrespect, sensitivity is defined as the moment generated for a given heelof the vessel.

Provision may also be made for controlling the movement of the floatingmember by braking means.

In an alternative arrangement shown in FIGURE 9, the cam surface may beprovided for example with gear teeth to engage the rollers of the floatwhich would take the form of pinions 4a, and suitable brakes 12 may befitted to brake the pinions and controlled from roll sensing means '13of known type. Alternatively, gears as described may be fitted inaddition to rollers which would carry the loading forces.

Variations in the tuning with amplitude can also be achieved; forexample, in FIGURE In, if instead of a uniform radius, a curve besubstituted in which the eflective radius at the centre portion isgreater or less than the radius at the sides then the periodic responseswill change with amplitude.

This feature and other features inherent in this novel tank design canbe used to alter the resonance curve and produce a resonance systemhaving a controllable band width of resonance.

Various other modifications may be made within the scope of theinvention. Thus, for example, under excessive seas, to prevent thefloating member violently striking the end of the tank in its movement,the curvature may be increased rapidly to provide a greater re-centeringforce for the buoyant member.

Again, the variations shown in FIGURES 3a and 5a allow for the buoyantmember to tilt as well as move in the translational sense across thetank, and this can be used to promote higher efliciency by forcing thebulk of the liquid to one'end and so achieve a greater stabilizingmoment. The buoyant member may also be suitably shaped to achieve thesame objectives.

For smooth operation of the floating member, it may also be fitted withrollers or wheels on the sides to guide it in the tank.

Variations can also be made in the shape of the tank system. Forefiicient stabilization of a given vessel a certain volume is requiredand this volume can be disposed either as a deep tank with smalldimensions in the fore and aft direction of the vessel, oralternatively, a shallow tank with correspondingly longer fore and aftdimensions, the law of movement required of the floating member beingmade the same in either case by suitably arranging the linkages or camand roller arrangement which guide and control the floating member.

The construction of the floating member may be of a rigid type utilisingmetal or such lighter material as fibre glass; alternatively, it may beof wholly flexible material such as rubber or plastic or constructedwith a combination of plastic and rigid members. The floating member mayin a further variant in construction be designed to keep its desiredshape by means of internal gas pressure.

In a further variation of the invention the movement of the floatingmember may be controlled either by positive means or by means of asystem such as a brake for dissipating energy or for holding the memberstationary, such action being initiated or controlled by a suitablesensor responsive to the movement of the vessel being stabilized.

I claim:

1. A tank system stabilizing a vessel against periodic rolling motioncomprising a tank containing a liquid; a buoyant member in said liquidand dividing said tank internally into two volumes which vary inverselyin dependence on the displacement of said buoyant member from a midposition in said tank; a passageway interconnecting said tank volumesand formed between said buoyant member and said tank; and tank tuningmeans in said tank partially determined by the height of said passagewaybetween said buoyant member and said tank and by guide means whichdefine a path of pronounced curvature along which said buoyant member isfreely movable during rolling motion of the vessel, said guide meansvarying the movement of said member from said mid position as a functionof the roll angle of the vessel.

2. A tank system as set forth in claim 1 in which said guide meanscomprise a track disposed above said buoyant member which is held by itsbuoyancy against said track.

3. A tank system as set forth in claim 2 further comprising verticaladjustment means controllably operable to vary the height of saidbuoyant member in said tank.

4. A tank system as set forth in claim 3 in which said verticaladjustment means produce vertical displacement of said track.

5. A tank system as set forth in claim 4 further comprising meanscontrollably operable to alter said pronounced curvature of said track.

6. A tank system as claimed in claim 1 in which said buoyant member is asphere.

7. A tank system as claimed in claim 1 in which said buoyant member is acylinder.

8. A tank system as claimed in claim 1 in which said tank is ofgenerally rectangular shape.

9. A tank system as claimed in claim 1 in which said buoyant member isconstrained by a curved roof on the tank.

10. A tank system as claimed in claim 1 in which said buoyant member issecured by at least one link to said tank.

11. A tank system as claimed in claim 10 in which said buoyant member issecured by parallel links to the bottom of said tank.

12. A tank system as claimed in claim 10 in which said buoyant member issecured by inclined links to the bottom of said tank.

13. A tank system as claimed in claim 1 in which said liquid has a freesurface.

14. A tank system as claimed in claim 1 in which the tank system isfilled.

15. A tank system as claimed in claim 14 in which the tank system isopen to the surrounding sea.

References Cited UNITED STATES PATENTS 3,083,671 4/1963 Ripley 114-124FQREIGN PATENTS 20,711 1914 Great Britain. 1,039,992 5/1953 France.

TRYGVE M. BLIX, Primary Examiner.

